The GWR had a surprising variety of Macaws = bogie bolster wagons. Some were shorter than was usual on the other railways and were popular for conversion by BR for use as crane runners. Diagram and other details taken from Atkins, A. G. Beard, W. Tourret, R. (1998) GWR Goods Wagons A historical survey. Tourret Publishing, Abingdon, Oxon. 530 pages ISBN 0-905878-07-8